Field of the Invention
The present invention relates to a wireless communication system for improving the handoff of wireless mobile devices, and in particular to a wireless communication system for improving the handoff of wireless mobile devices according to geographic information.
Description of the Related Art
In the modern wireless communication system, a wireless mobile device scans a service station within the region where the wireless mobile device is located according to a scanning-station period pre-stored in the wireless mobile device, and registers at a system service server through the scanned service station. For example, when the wireless mobile device scans a first service station, the wireless mobile device registers at the system service server through the first service station. In addition, the wireless mobile device obtains the signal strength provided by the service station within the region where the wireless mobile device is located, according to the result of a scanning station.
When the wireless mobile device scans the first service station and a second service station, the wireless mobile device may be located, for example, in the overlapping service range of the first service station and the second service station. The wireless mobile device then separately compares the signal strength provided by the first service station and the second service station with a threshold handoff value pre-stored in the wireless mobile device. When the signal strength provided by the first service station is higher than the threshold handoff value and the signal strength provided by the second service station is lower than the threshold handoff value, the wireless mobile device does not hand off to the second service station. In contrast, when the signal strength provided by the first service station is lower than the threshold handoff value and the signal strength provided by the second service station reaches the threshold handoff value, the wireless mobile device hands off to the second service station.
Accordingly, the wireless mobile device determines whether to perform the handoff or not by comparing the threshold handoff value with the signal strength provided by the stations. However, a failure of the wireless mobile device to hand off may still occur. For example, when the first service station cannot provide sufficient signal strength for the wireless mobile device and the wireless mobile device still does not register at (and hand off to) the second service station, the handoff failure occurs. In more specific terms, because the wireless mobile device scans the service stations according to the scanning-station period pre-stored in the wireless mobile device, when the wireless mobile device proceeds away from the first service station at a rapid rate, the wireless mobile device cannot receive sufficient signal strength from the first service station anymore. In addition, because the wireless mobile device does not perform scanning before the next scan and thereby does not register at the second service station, the handoff failure occurs. The remaining situation, such as a handoff delay (it takes time for the wireless mobile device to register at (and hand off to) the stations), the smaller intersection of the service range between the first service station and the second service station results in the handoff failure.
Moreover, because the scanning-station period pre-stored in the wireless mobile device is a fixed period, the wireless mobile scans the service station according to the fixed period no matter whether the wireless mobile device is near the service station or not, or whether the wireless mobile device moves or not. Thus, it leads to higher power consumption or a handoff failure.
Therefore, it is required to provide a new handoff method and a wireless communication system using the same. When the wireless mobile device is near the service station, the wireless mobile device scans the service station according to the longer scanning-station period, or when the wireless mobile device proceeds away from the service station, the wireless mobile device scans the service station according to the shorter scanning-station period so as to resolve the problems of higher power consumption or the failure of handoff.